Analog Devices Inc./Maxim Integrated MAX6840XSD4

Overview

The MAX6840XSD4 from Maxim Integrated is an ultra-low-voltage microprocessor supervisory circuit with open-drain active-low reset output, adjustable RESET-IN threshold (444mV typical), 1.68s reset timeout period, and operation down to VCC = 1.1V. It monitors supply rails in portable and battery-powered systems by asserting reset when RESET-IN falls below threshold, supporting bidirectional µP reset interfaces via its open-drain architecture.

For engineers reviewing the MAX6840XSD4 datasheet, MAX6840XSD4 pinout, MAX6840XSD4 application, or MAX6840XSD4 equivalent, key selection criteria include its 4-pin SC70 package, ±3.0% RESET-IN threshold accuracy over temperature, 7.5µA supply current, and compatibility with external resistive-divider voltage monitoring networks.

Technical Context

The MAX6840XSD4 uses a high-impedance RESET-IN input (444mV reference) to monitor externally divided supply voltages, enabling precise trip-point configuration for supplies as low as 0.44V. Its reset comparator ignores fast transients and guarantees valid reset assertion down to VCC = 0.55V.

It features an open-drain active-low RESET output requiring an external pullup, allowing level-shifting across supply domains (e.g., 1.2V monitored rail to 3.3V or 5V reset logic). The fixed 1.68s timeout (D4 suffix) ensures sufficient hold time for complex power-up sequencing in embedded controllers.

Key Specifications

Pinout & Package

MAX6840XSD4 is housed in a 4-pin SC70 package (2.0mm × 2.1mm, 0.5mm pitch), optimized for space-constrained portable designs. Pin 1 is RESET-IN, Pin 2 is VCC, Pin 3 is GND, and Pin 4 is RESET (open-drain active-low).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar microprocessor supervisory applications.

Compared with MAX6837XSD4 and TLV809K33DBZR, the MAX6840XSD4 uniquely supports externally adjustable thresholds down to 0.44V and delivers the longest standard timeout (1.68s), making it optimal for complex, multi-stage power-up sequences in ultra-low-voltage embedded systems.

Availability

MAX6840XSD4 is available at Aetrix Electronics and suitable for portable medical devices, industrial sensor nodes, wearable electronics, and edge AI modules requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for MAX6840XSD4 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Maxim Integrated (now part of Analog Devices) designs precision analog, mixed-signal, and power management ICs for demanding industrial, automotive, and communications applications.

The MAX6832–MAX6840 family delivers ultra-low-voltage supervisory circuits targeting battery-powered and energy-constrained embedded systems requiring high accuracy, minimal quiescent current, and flexible reset configuration.

FAQ

What is the function of the RESET-IN pin on the MAX6840XSD4?

The RESET-IN pin on the MAX6840XSD4 is a high-impedance input referenced to a 444mV internal threshold. It enables external voltage monitoring via a resistive divider network-reset asserts when the voltage at RESET-IN falls below 444mV. This allows the MAX6840XSD4 to supervise supply rails as low as 0.44V while operating from a higher VCC (1.1V–3.3V), making it ideal for multi-rail systems where direct VCC monitoring is insufficient.

Does the MAX6840XSD4 require an external pullup resistor on the RESET pin?

Yes, the MAX6840XSD4 features an open-drain active-low RESET output and requires an external pullup resistor to define the logic-high state. The pullup may connect to any voltage between 0V and 6V-including supplies different from VCC-enabling level-shifting. Typical values range from 10kΩ to 100kΩ depending on rise-time and bus loading requirements. Without this pullup, RESET cannot achieve a valid HIGH state.

What is the significance of the 'D4' suffix in MAX6840XSD4?

The 'D4' suffix in MAX6840XSD4 specifies a nominal reset active timeout period of 1680ms (1.68 seconds). This fixed delay begins after RESET-IN rises above the 444mV threshold and ensures the reset signal remains asserted long enough for complete microprocessor initialization, memory clearing, and peripheral configuration-even in systems with slow-ramping or multi-stage power supplies.

Can the MAX6840XSD4 operate with a VCC lower than 1.1V?

No-the MAX6840XSD4 requires VCC between 1.1V and 3.3V for guaranteed operation. While the RESET-IN input can monitor rails as low as 0.44V, the device itself needs ≥1.1V on VCC to maintain specified threshold accuracy (±3.0%), timing performance, and internal biasing. Operation below 1.1V violates the Absolute Maximum Ratings and may result in undefined behavior or failure to assert reset correctly.

How does the MAX6840XSD4 handle noise on the RESET-IN line?

The MAX6840XSD4 incorporates inherent noise immunity on the RESET-IN line through its comparator design and 0.75% hysteresis around the 444mV threshold. For environments with significant EMI or long PCB traces, adding a small capacitor (e.g., 100pF–1nF) from RESET-IN to GND provides additional filtering without compromising response time. The device's high input impedance (>100MΩ) also minimizes current-driven noise coupling.